At least with I2C we have the option to use stronger pull-ups and lower
speed for noisy cases. For USB there's no such option and cables are
limited to 5 meters for USB FS and 3 meters for USB LS.
--------------8<--------------8<-------------
*Ronan Paixão*
2011/12/7 Bruce Perens <br...@perens.com>
> On 12/07/2011 03:21 PM, Ronan Paixão wrote:
>
>> For example, the Idle current on the $4.40 Atmega32u2, an AVR
>> microcontroller which has USB support, is ~250uA@1MHz, with as little as
>> 4.6uA on Power-down. Probably add a little for the USB peripheral.
>>
> The power drain is going to be the cost of bus signalling. There's a short
> discussion at
> http://www.beyondlogic.org/**usbnutshell/usb2.shtml<http://www.beyondlogic.org/usbnutshell/usb2.shtml>
>
>
>> For simplicity's sake and easy hardware implementation and availability,
>> I'd go for I²C support.
>>
> Except that then we have to implement new software to drive devices on I²C
> that are already really well-handled on USB.
>
> Atmega48PA, with 7uA@128KHz/2V on Idle, including the Internal RC
>> Oscillator.
>>
> For I²C on the 10-foot cable they use for dance-pads, there is a power
> cost for driving the bus. It's not going to be really high impedance,
> low-power-drain, without having noise problems.
>
> Thanks
>
> Bruce
>
>
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